This document discusses growing a winter garden and using season extenders to extend the growing season. It provides information on different types of season extenders including hot caps, floating row covers, cold frames, low tunnels, high tunnels, and greenhouses. These season extenders work by trapping heat and protecting plants from cold temperatures and wind. The document recommends starting cold-tolerant crops in late summer and fall and choosing protected garden beds and season extenders to successfully grow vegetables through the winter.

1. For many of us, when the curtain
of frost falls on our summer
vegetables, we put away our
tools and wait for spring to begin
again. But it is possible to have a
second act with a whole new cast
of characters. Growing a winter
garden is a great way to continue
to enjoy fresh, healthy vegetables
throughout the year. With a bit of
planning and a few winter-specific
approaches, you can successfully
grow vegetables that are as varied
and tasty as anything summer has
to offer.
The guru of winter vegetable
gardening, Eliot Coleman, is a
market gardener on the coast
of Maine. If he can grow winter
vegetables profitably there, it
should be easy here in the foothills
of Nevada County.
In many respects, your winter
garden will take less work than
the summer version. You will not
need to water as often. Weed
and bug problems are fewer. The
key is getting started early and
planting cold-tolerant varieties.
Mature plants can withstand cold
temperatures better than younger
plants. Most of the plants you will
grow in winter such as lettuces,
leeks, onions, mache and kale,
can survive temperatures into the
teens or even single digits once
established, especially if given some
protection. A well-hydrated plant
will handle the cold better than
one that is drought stressed. So,
be prepared to water if there is an
extended dry spell in the winter.
Choosing beds that are protected
from the prevailing winter wind will
also help.
I have managed to have a
respectable winter garden for
several years. Our nighttime
temperatures on clear nights
are generally in the low 20s
with excursions into the teens
a few times during the winter
being predictable. The lowest
temperature I have recorded at
our place was 10F, and our winter
garden pulled through in decent
shape.
One of the big challenges to
growing a winter garden is figuring
out where to put it. Many of your
winter vegetables will need to be
planted in July, August or early
September—when your summer
crops are still producing well. You
can never have too many garden
beds, and this is a good argument
for establishing more. You’ll find
that the rotation is actually fairly
simple if you plan ahead. You may
have a summer cover crop such
as buckwheat on some beds, just
waiting for your winter vegetable
starts. Beds that had peas in the
winter and spring are also likely
candidates. Instead of winter cover
crops or straw on all of your beds,
some will be growing salad and a
vegetable side dish. If you live in
snow country, you will probably
need to use a season-extender
structure. You will also need to clear
the snow away to allow enough
light to reach the plants. The
exception would be root crops such
as beets and carrots. If you plant a
sufficient number in the spring, you
can enjoy them all winter. Unless
your soil freezes, mature beets and
carrots will do just fine under the
snow waiting to be pulled up for
dinner. But the spring planted crop
will not be as sweet as those you
plant in the late summer or early fall
after the frost hits them.
The following chart includes
hardy vegetables you may want to
consider growing and the number
of days to plant prior to your
first frost date. It is by no means
a complete list. This information
came from Eliot Coleman’s book
Four Season Harvest with some
modifications based on my
experience. Of course the best
planting date depends on whether
the cold settles hard in the fall at
your garden site or if you tend to
have a period of warmer weather
after the first frost.
Sequential planting through the
period will extend your harvest
Your Winter Vegetable Garden
The Second Act
Mike Kluk, Nevada County Master Gardener
Nevada County Master Gardeners (530) 273-0919
http://ncmg.ucanr.org 255 S. Auburn St., Grass Valley CA
UCCE Nevada County Master Gardeners

2. although that is not a big issue
for a winter garden because the
plants mature slowly. If you use
the covers discussed in the next
article, you can plant in the shorter
time frame. If you don’t, you should
start your plants near the earlier
date. In any case, mustard, in all of
its manifestations—from broccoli
to tatsoi—is likely to be the star of
your winter garden.
Site selection to take advantage of
the warmest microclimates in your
garden important. For example,
areas near a south-facing fence
or wall will benefit from reflected
heat and light during the day.
Concentrating your winter garden
in areas that are protected from
cold, drying winds will also go far
to increase your plants’chances of
surviving the winter.
Vegetable Varieties for the Winter Garden
Direct seed Days before first frost
Beets 30-60
Carrots 45-60
Cilantro 20-60
Claytonia (Miner’s Lettuce) 15-45
Lettuce (leafy cut and come again 15-70
varieties seem most successful)
Mache (Corn Salad) 15-45
Peas 45-90
Scallions 15-90
Spinach 0-30
Swiss chard 30-60
Turnips 45-60
Seed Transplant Starts
(Plant out approx. 30 days after seeding)
Broccoli 75-105
Cabbage 60-90
Cauliflower 75-105
Kale (Red Russian) 45-105
Leeks 90-120
Mustard Greens, Boc Choy,
Pak Choy, Mizuna, Tatsoi 15-75
Parsley 45-90
References: The Winter Harvest Handbook and Four-Season Harvest, Eliot Coleman
Gardening When It Counts—Growing Food in Hard Times, Steve Solomon
Winter Gardening in the Maritime Northwest: Cool-Season Crops for the Year-Round Gardener, Binda Colebrook
How to Grow Winter Vegetables, Charles Dowding
Solar Gardening—Growing Vegetables Year Round the American Intensive Way, Leandre Poisson/Gretchen Vogel Poisson
The Art of Season Extending, University of California Cooperative Extension

3. Season Extenders
Maybe You Can Fool Mother Nature
Mike Kluk, Nevada County Master Gardener
The phrase“season extender”
refers to a wide range of generally
low-tech items and approaches
that can keep your warm-season
plants warm when it’s cold
outside and your cool-season
crops cool when the mercury is
rising.
Season extenders will not fool
Mother Nature enough to let you
grow tomatoes in the winter or
most lettuces in the height of
summer. But season extenders
can help you get a jump start
on your summer garden, keep
your cool-weather crops going
longer into the summer, extend
your summer vegetables deeper
into fall and grow cold-tolerant
vegetables through winter.
Some common season extenders
are cloches or hot caps, low
tunnels with coverings of
polyethylene plastic or row
cover, cold frames, high tunnels,
greenhouses and shade cloth.
This article will give you an
introduction to the most
common season extenders and
hopefully inspire you to give
them a try.
Fall and spring
season extenders
The early spring is a time of
changeable, fickle weather in the
foothills. Season extenders make
it possible to start warm-season
crops at times that would not
otherwise be optimum. Home
gardeners are most familiar
with the season extenders
used in spring. All of them work
on the principle of creating a
microclimate by holding in the
heat of the sun and humidity
during cold days and protecting
the plants from damaging winds.
At night, they hold in some of the
heat stored in the soil during the
day, not letting it escape to the
atmosphere as fast as it otherwise
would.
Hot caps
Over 350 years ago, gardeners
discovered that they could
protect heat-loving summer
varieties from late frosts by
covering each individual plant
with a small oiled paper tent
or a large“jar”made of glass,
often called a cloche or bell
jar. Gardeners still use these
although they are most often
made of thin plastic supported
by a wire hoop or homemade
out of a plastic milk jug with the
bottom cut off. Unfortunately,
these individual coverings must
be removed on warm sunny days
to avoid overheating the plants
and, because of the small size,
can have only a limited affect on
nighttime temperatures.
Floating row cover
Another spring option is row
cover, generally spun polyester,
which is laid directly on the plants
and held down on the edges
with soil or rocks. Floating row
cover serves the same function of
increasing daytime temperatures
and humidity when necessary
and holding some of the day’s
heat in at night for at least a while.
It has the added benefit that it
Nevada County Master Gardeners (530) 273-0919
http://ncmg.ucanr.org 255 S. Auburn St., Grass Valley CA
UCCE Nevada County Master Gardeners
A greenhouse—the biggest, most expensive type of season extender

4. breathes”so that it is unlikely to
overheat on sunny, warm spring
days. The material used in this way
is a thin version of row cover. The
various covering options will be
discussed separately below.
Hot caps and floating row cover
work in the relatively warm days
and nights of late spring. Floating
row cover is a practical way to
protect your mature summer
vegetables from the first cool
nights of fall, extending your
harvest of cucumbers, squash
and tomatoes. However, these
season extenders provide little
protection from frost or freezing
temperatures. Floating row cover
will freeze to the plants it is laying
on during an icy night, providing
no real protection.
Late fall and winter
season extenders
In general, the more area you
can enclose in a structure, the
more efficiently it will maintain
an environment of somewhat
higher temperatures and humidity
that will help your plants make it
through tough weather. Larger
and more substantial structures
will provide more protection than
hot caps and floating row cover.
They will hold heat longer, shelter
from stronger winds and protect
from the effects of direct frost.
They will allow you to grow cold
weather plants and vegetables
such as kale and lettuce through
the winter in the foothills without
an external heat source except
the sun. But they will not maintain
an environment that will support
warm-weather plants such as
tomatoes or squash far into the
cold days of late fall without a
heater or fairly elaborate system
of heat storage. Both of those
options are beyond the scope of
this article.
Cold frames and low tunnels
The next step up in effectiveness,
beyond floating row cover, is a
cold frame or, its more modern
cousin, the low tunnel. Traditional
cold frames are constructed
of wood with a hinged glass
covering. They are generally
oriented with the long side
running east/west. The south
edge is typically lower than the
north to allow better access to
the low winter sun. Cold frames
can be purchased at many garden
supply stores. They can also be
built by anyone with even modest
building skills. You can even
construct the sides of a“frame”out
of straw bales. Fill the center part-
way with soil and cover it
with a clear panel and you
have a serviceable cold
frame.
If you hinge one side
of the cover, the cold
frame must be narrow
enough to allow you to reach
all of the plants from the open
side. An alternative is to use 4’x
8’polycarbonate panels that are
simply laid on the frame. They
will span a typical garden bed,
can be held down with boards or
bricks and simply slid off when
you want access. Cold frames have
the disadvantage of being fairly
expensive to buy and somewhat
complicated to build and may
not be practical to cover multiple
beds.
Low tunnels are easy to construct,
and covering several beds is quite
feasible. They are simply a series
of hoops, stuck in the soil or fixed
to a raised bed, that form a tunnel
down the length of the bed.
Putting a hoop every three or four
feet is generally adequate. The
hoops can be constructed from
any material that can be bent into
a hoop shape. Some nurseries sell
heavy-gauge wire in sections that
is designed to be bent into hoops.
However constructing hoops from
rebar or ½”PVC or thin-wall metal
conduit can result in a stronger
structure. To protect against wind
damage, it is useful to tie or
screw a section of pipe
to the top of the
hoops, running
the length
of the bed.
If you get
substantial
snow, it
may also be
necessary
to cut short
sections of board or
pipe that can be set vertically to
support the hoops. Once your
hoop structure is in place, a cover
is then laid over it. The cover
Low tunnel
More low tunnels

5. should be large enough to cover
both ends and sides to the ground
with some extra. Cover and
securing options will be discussed
below.
High tunnels or hoop houses
A high tunnel or hoop house is
a bigger and more substantial
version of a low tunnel. It can span
the width and length of several
garden beds or more. Given its
greater size, the construction
needs to be more careful and
beefier. A common choice for
hoop material is 1¼”PVC pipe. But
the principal is the same: using
the inherent strength in a series
of arches to support a cover that
will maintain a relatively warm
and protected environment for
your plants. The end walls of the
“tunnel”are typically constructed
of 2 x 4s. A door for access and
windows for venting are added. In
heavy snow areas, these structures
can be strengthened with a 2 x 4
placed vertically supporting each
hoop. Hoop houses sometimes
even have a double wall of plastic
sheeting with air blown between
them for insulation but such an
elaborate system is not necessary
in our climate to provide adequate
protection for cold-hardy plants
such as broccoli or Swiss chard. It
is helpful to not attach the cover
permanently to the lower 3–4 feet
of one side so that it can be rolled
up on a hot day.
Greenhouses
You can buy prefabricated
greenhouses at most garden
supply stores. In addition,
automatic window openers,
fans and other accessories make
greenhouses very adaptable to
various climates and seasons.
Greenhouses can also be custom
designed and built out of new
or used materials. Greenhouses
are typically more complicated
to construct than hoop houses
but can be a more permanent
structure.
A very serviceable greenhouse
can be made from a metal
carport structure, often available
used, that is then covered with
polyethylene plastic. People who
live in snow country may want to
use polycarbonate or fiberglass
panels for the roofing. Plants in
a winter greenhouse should be
planted in the ground where
they will be much warmer than
if planted in pots on benches.
For added protection, you can
add low tunnels over the plants
within the greenhouse. You can
also put barrels of water in the
greenhouse as an added reservoir
of daytime heat that will moderate
temperatures at night.
Coverings
Your choice of covering material
will be dictated by a number of
factors; cost and practicality being
chief among them.
Glass or polycarbonate. If you
live in an area that gets heavy
snow, your best choice is glass
or polycarbonate panels. Glass
can be expensive, although used
windows are generally cheap or
free. Polycarbonate panels are also
pricey but will last many years,
and as stated above, can cover an
almost 4’x 8’bed.
Polyethylene plastic. Polyethylene
is the traditional cover for low
tunnels and hoop houses. If you
use this, purchase greenhouse
plastic (not regular“construction”
plastic) that is at least 6 millimeters
thick. It will resist deterioration by
UV light and should last five years
or longer if you protect it from the
sun when not in use during the
summer. You can also get plastic
that has an additive to increase its
ability to reflect heat. Polyethylene
is tough and will work fairly well
in snow country if you are able to
clear it after each snow fall.
The big disadvantage of the rigid
cold frame covers or polyethylene
is that they do not vent to keep
heat from building up during
sunny days, possibly cooking
your vegetables prematurely. For
tunnels, you will need to be able
to roll up at least one side to vent
the structure on any sunny day
warmer than about 45F. There are
automatic openers available for
cold frames. Although that adds
expense, it makes them practical
for people not able to open and
close them during the day.
Row cover and Dio-Betalon. The
need to vent a tunnel is solved
by using row cover or a product
made from polyvinyl alcohol
marketed as Dio-Betalon (formerly
Tuffbell.) Both are porous enough
to allow built-up heat to escape.
Even though porous, on a freezing
night, frost will form on the
surface, closing off the holes and
creating a snug environment for
your vegetables.
Row cover comes in multiple
thicknesses. The version that
Low tunnel with row cover

6. blocks out 30% of the light
seems to be a good compromise
between protection and light
availability in the winter. It lets in
enough light for hardy plants to
do fine during our winters that
generally feature quite a lot of sun
yet it offers meaningful protection.
If you anticipate a particularly
cold night, you can throw on an
additional layer. One disadvantage
of row cover is that because it is
opaque, it is easy to“forget”to
attend to your vegetables—out of
sight out of mind.
Dio-Betalon is clear. It lets in
more light than row cover and
the plants within are visible. The
primary disadvantage of Dio-
Betalon is cost. A piece large
enough to cover two 4’x 8’beds
costs about $100 locally.
If you use one of the flexible
covering materials such as
polyethylene or row cover, you
will need to secure it to the hoop
structure. This can be done by
leaving enough trailing on the
ground to hold down with rocks
or shovelfuls of soil.
A much more convenient means
of connecting the cover to the
hoops are plastic clips specially
made for this purpose (available
from garden supply stores) or
large binder clips (available from
stationary stores.) In any case, be
sure that the ends and sides are
securely sealed to prevent cold air
from blowing in.
Whatever structure and cover
combination you choose, the
added protection will allow you
to grow cold-tolerant vegetables
through the winter in western
Nevada County. A hot soup rich
with vegetables and a salad, all
from your back yard, can brighten
the coldest winter day.
Summer season extenders
As the weather warms into
summer, you may want to
extend the season for your cool-
season vegetables. In that case,
protecting plants from the harsh
direct rays of the sun is the key.
This can be done with some
success by planting in an area that
will get afternoon shade. But that
will probably not be enough in
itself to protect your crop of kale,
rapini or lettuce as summer ramps
up.
Shade cloth is the most practical
tool to use to bring summer
relief to your cool-weather crops.
Shade cloth comes in a variety
of“weights”that will block out
more or less sun, but also light. If
shade is too heavy, it will stunt or
kill even the toughest of winter
vegetables. A cloth that blocks out
50% of the light seems to strike
about the right balance in our
environment.
Shade cloth is either woven or
knitted. The woven must be
hemmed to prevent it from
unraveling. The knitted is generally
cheaper and has the advantage of
not unraveling when cut. Thus you
can buy it in bulk and simply cut
off a piece the size and shape you
want.
If you have constructed low
tunnels, you can use the same
structure to support the shade
cloth. The same clips will hold
it on. Shade cloth in itself will
generally extend the season
of your favorite cool season
vegetables into summer.
If you add a water system that
mists from above, you will get an
added measure of protection. If, in
addition, you grow heat tolerant
varieties of kale, lettuce and other
cool-season crops, you will be a
long way down the road to having
fresh salads and greens in the
summer.
Other plants can benefit from
shade as well. Raspberries and
some blackberries suffer from
our hot summer days but will do
better if grown under shade cloth.
Mint is always a candidate for a
little shade. Even basil, the queen
of high summer herbs, will have
bigger leaves and more tender
stems if grown under shade cloth.
If you combine the summer and
winter season extenders discussed
in this article, your vegetable
garden will be more varied and
more productive through the
year. Your own home-grown
vegetables are, after all, the
freshest and most local you will
ever eat.
Nevada County Master Gardeners (530) 273-0919
http://ncmg.ucanr.org 255 S. Auburn St., Grass Valley CA
UCCE Nevada County Master Gardeners
Sources
California Master Gardener Handbook, Univ. of Calif. Agriculture and Natural Resources, pub. #3382, pp 343-343
Season Extenders, http://urbanext.illinois.edu/hortihints/0402c.html
Low Tunnels, http://extension.psu.edu/plants/plasticulture/technologies/low-tunnels
How to Make a Low Tunnel in Pictures, http://sites.duke.edu/farm/2012/11/10/how-to-make-a-low-tunnel-in-pictures/
Season Extenders, Virginia Cooperative Extension, Environmental Horticulture, pub. # 426-381